The uses for point-to-point linear transfer devices are numerous, i.e., where it is desired to convert rotary motion to linear motion on an economical basis. Typical applications for such linear transfer devices include loaders and unloaders for machine presses, transfer devices for automated machine tools and welding lines, and the like. In such devices the rotating drive cams or screws are held stationary, while the cam followers are mounted on a moveable carriage. Thus, with such prior devices, the cam would have to run the full length of the linear slide mechanism. This would necessitate expensive elongated cam structure; further, such elongated cams inherently had a high moment of inertia requiring large drive motors in order to actuate them.
Several prior mechanisms have been utilized to effect such linear movements. One type prior art linear drive actuator utilized a conventional acme screw mechanism, i.e., a large diameter lead drive screw running the full length of the actuator. Another prior device was the so-called ball screw mechanism, where again the rotating shaft was maintained stationary, and the ball screw slide would move linearly relative to the shaft. However, such ball screw mechanisms have substantial speed limitations, i.e., typically in the range of 500 r.p.m. or less. Also, such ball screw type linear actuators have a relatively low load capacity. Another type prior device was the so-called band-type linear actuator, where a flexible band member, connected at each end to a tooling slide plate, was entrained about two or more drive wheels.
One significant disadvantage with most prior cam-driven linear slide devices was that, because they utilized a relatively few number of cam roller followers, which were in continuous engagement with the drive cam, the life expectancy of such roller followers was very limited. Additionally, with most prior cam-driven linear actuator designs, it was often required to virtually dissemble the moveable load carriage assembly when a cam follower needed to be replaced, as the same were typically carried within the load carriage. Further, most acme or ball screw type prior devices inherently required a high reduction ratio; thus, they had to run at very high speeds or for excessive rotations just to produce the desired linear actuation motion.